Danian-lower Selandian Microcodium-rich calcarenites of the Subbetic Zone (SE Spain): Record of Nereites ichnofacies in a deep-sea, base-of-slope system

Abstract

The Olivares Formation, a lower Paleogene unit of the Subbetic Zone in Southern Spain, is mostly composed of calcarenites comprising 60–90% of resedimented Microcodium remains, which are intercalated in hemipelagic marls rich in planktonic foraminifera. Microcodium is formed on the roots of terrestrial plants adapted to live on carbonate-rich substrates, its occurrence in the Olivares Formation entailing a massive resedimentation from a subaerially exposed carbonate source area. New field observations demonstrate that the unit was deposited, at the base of a faulted slope, within a graben flanked by massifs of mostly Jurassic carbonates, while an ichnological analysis shows an abundant and moderately diverse trace fossil assemblage consisting of 30 ichnospecies belonging to 21 ichnogenera. The nongraphoglyptid assemblage (24 ichnospecies, 16 ichnogenera) is dominated by Chondrites, Ophiomorpha, Planolites, and Scolicia. Zoophycos isp. is common, while Cladichnus, Gordia, Helminthopsis, Multina, Nereites, Parahaentzscheliana, Polykampton, Spirophycus, Strobilorhaphe and Thalassinoides isp. are scarce or rare. In the graphoglyptid assemblage (6 ichnospecies, 5 ichnogenera), Helminthorhaphe is common/scarce and Belorhaphe, Desmograpton, Paleodictyon and Urohelmintoida are scarce/rare. This trace fossil assemblage, with abundant Scolicia and Nereites and frequent graphoglyptids, can be assigned to the deep-seaNereites ichnofacies. Within the Nereites ichnofacies, the Ophiomorpha rudis and Paleodictyon subichnofacies are readily differentiated, and the Nereites subichnofacies probably also occurs, pointing to vertical changes in the turbiditic system most likely related to a coeval sea-level rise that eventually resulted in the flooding of the emergent Microcodium-producing carbonate massifs.